The invention relates to a method for determining the web tension or the web tensile force in a printing substrate web. In addition, the invention relates to a device for determining web tension or the web tensile force in a printing substrate web.
In web-fed rotary printing presses, a to-be-printed printing substrate web is normally drawn off by a printing substrate roller that is held in readiness in the area of a reel changer, transported through printing couples for printing and, after printing, conveyed to a folding unit for further processing. So-called drag rollers as well as so-called web guide rollers are used to transport the printing substrate web through the web-fed rotary printing press. Drag rollers are driven by drives that are assigned to the drag rollers. No drives are assigned to web guide rollers. In fact, web guide rollers are carried along by friction from the printing substrate web.
For proper operation of a web-fed rotary printing press it is necessary to know the web tension in effect in the printing substrate web or the web tensile force in effect in the printing substrate web at defined positions along the transport path of the printing substrate web through the web-fed rotary printing press. The web tensile force is a force, wherein a web tension is determined from the web tensile force when the web tensile force is divided by the width of the printing substrate web being webbed up.
In web-fed rotary printing presses known from practice, each position of the transport path of the printing substrate web, for which the web tension or the web tensile force must be determined, is assigned a device, which supplies a signal that makes it possible to deduce the web tension in effect at the respective position or the web tensile force in effect at the respective position. Consequently, it is necessary to determine the web tension or the web tensile force at a position downstream from a drag roller as well as at a position upstream from a drag roller, as viewed in the transport direction of the printing substrate, and therefore each of these two positions are assigned such a device and thus a measuring point. This is involved and expensive.
Starting herefrom, the present invention is based on the objective of creating a novel method and a novel device for determining the web tension or the web tensile force in a printing substrate web.
According to the invention, the web tension in effect at a second position along the transport path of the printing substrate web or the web tensile force in effect at the second position is determined arithmetically, namely from the web tension in effect at the first position or from the web tensile force in effect at the first position as well as from forces, which at least one driven roller and/or at least one trailing roller, which is/are arranged along the transport path of the printing substrate web between the first position and the second position, introduce to the printing substrate web.
The present invention provides for the first time that the web tension in effect at a position along a transport path of the printing substrate web or the web tensile force in effect at this position be determined arithmetically, and namely on the basis of the web tension in effect at another position along the transport path of the printing substrate web or the web tensile force in effect at the other position as well as on the basis of forces, which at least one driven roller and/or at least one trailing roller, which is/are arranged along the transport path between these two positions, introduce to the printing substrate web. This makes it possible to reduce the hardware-related expense and to determine the web tension and thus the web tensile force at positions along the transport path of the printing substrate web through a web-fed rotary printing press with lower expense and therefore more cost-effectively.
Preferred developments of the invention are yielded from the following description. Without being limited hereto, exemplary embodiments of the invention are explained in greater detail on the basis of the drawings.